In networks of today for wireless radio communication, it is common to use a shared radio resource for communication of radio signals between various different nodes capable of radio communication such as access points, base stations, wireless devices, Machine-to machine (M2M) devices, relay stations, depending on the terminology used. In this description, the term “station” will be used to generally denote a node capable of radio communication. The shared radio resource may be defined by frequency, time and/or code which is well-known in this field. This means that when a radio signal, e.g. comprising a data packet, is transmitted by a transmitting station on the shared radio resource, this radio signal can be detected and received by any station located within “hearing” distance from the transmitting station and monitoring the shared radio resource. Any station that detects and receives the radio signal is therefore required to determine whether the transmitted radio signal is intended, i.e. targeted, to be received and used by that station or not.
FIG. 1 illustrates a typical communication scenario for such a procedure, involving a transmitting station 100 that transmits a radio signal, e.g. comprising a data packet, which is intended to be received and used by another station 102 which can thus be called the “targeted station”. The transmitting station 100 may be any of the above-mentioned types of nodes. In this example, there are three other stations, generally indicated by numeral 104, which are located within an area where the transmitted radio signal can be “heard”, i.e. detected and received. The stations 104 can therefore be called “receiving stations” and the targeted station 102 is effectively also a receiving station in this context.
It is thus assumed that the targeted station 102 and the other receiving stations 104 are able to receive the radio signal, e.g. as transmitted on a shared radio resource which is monitored by the stations 102, 104, but none of them knows initially to which station the signal is targeted until they have decoded the radio signal and read a destination identity or address in the signal which indicates station 102 as the intended receiver, i.e. target, of the radio signal. As a result, the targeted station 102 will proceed to use the received radio signal in some sense depending on its content, while the other stations 104 will simply discard or ignore the received radio signal since it was not directed to them. For example, the radio signal may contain data and/or signaling message directed to the targeted station 102 alone in this example. In other examples, a radio signal may be directed to more than one targeted station at the same time and throughout this description the term targeted station should be understood as at least one targeted station.
At least some of the receiving stations 102, 104 may be powered by a power source with limited capacity and lifetime such as a battery, which is common for handheld wireless devices and for M2M devices such as sensors, and such stations can be referred to as power limited stations. It is a problem that power is consumed in the receiving stations 104 for receiving and decoding the radio signal only to find out that it is directed to station 102. The received and decoded radio signal is thus useless to stations 104 and power has been consumed to no avail, only draining each stations' power source which may reduce its lifetime.
This problem can thus be significant for stations that are power limited and/or have requirements for a long battery lifetime, particularly when there are frequent transmissions of radio signals in the area and when the transmitted radio signals are of considerable length often having the target address or identity placed close to the end of the packet. In addition, a checksum for a data packet containing some payload is typically taken over the entire payload which must thus be decoded to confirm that the packet has been received correctly according to the checksum.